A propylene resin is one of the resins that have been widely used to produce containers for goods such as detergents, shampoos, drinks, foods and medicines. Almost all of the containers are obtained according to a blow molding method, which method is well known in the art as a production method for thermoplastic resin made containers. The blow molding method can be classified into (i) a direct blow molding method using a hot parison, and (ii) an injection-stretching blow molding method using a hot parison or a cold parison. The former molding method is superior in its molding stability and its cost of molding equipment when compared to the latter molding method. Therefore, many of polypropylene resin made containers are obtained according to the former molding method.
A polypropylene resin has a defect of poor impact resistance in spite of its superior heat resistance, rigidity and transparency. Therefore, there have heretofore been proposed some compositions which are improved in their impact resistance without detrimental effect on superior transparency of the polypropylene resin. As such compositions, there are known a composition comprising a polypropylene resin, a straight chain low-density polyethylene and an ethylene-.alpha.-olefin copolymer elastomer (JP-B 5-88264); an ethylene based copolymer composition comprising an ethylene-.alpha.-olefin copolymer polymerized using a metallocene catalyst and a crystalline polyolefin (JP-A 8-283476); and a composition comprising a polypropylene resin and an ethylene-.alpha.-olefin copolymer polymerized using a metallocene catalyst (JP-A 9-31264). Each of the references referred to above is incorporated herein by reference in its entirety.
However, blow-molded containers obtained using any of the compositions mentioned above have a problem such that the impact resistance thereof in terms of a falling strength is far from a satisfactory level.
Moreover, the aforementioned compositions per se have a problem such that they are not satisfactory in their moldability. That is, a die swelling ratio is greatly changed under conditions where a shear rate is greatly changed, for example, (i) when blow molding conditions such as extruder output are altered, or (ii) when a die gap is altered in order to prevent an uneven thickness caused by draw down of the resin, or (iii) when a die gap is altered in order to prevent an uneven thickness caused by a shape of the molded product, and as a result, a thickness variation of a parison is increased.